Electric fuses are generally used in various semiconductor devices as nonvolatile storage elements.
For example, an electric fuse is used as a nonvolatile storage element for holding recovery data for a redundant memory, identification data inherent in a chip, encrypted data for security, or trimming data for adjusting a voltage or timing in an internal circuit.
For example, the electric fuse is cut off and the resistance value of the electric fuse changes by causing a current to flow therethrough. For example, when the electric fuse is used as a nonvolatile storage element, the electric fuse is not cut off to write data “0” and is cut off to write data “1.”
The data “0” and “1” may be set reversely. For example, the electric fuse may be cut off to write data “0” and may be not cut off (may remain unchanged) to write data “1.” The electric fuses for writing data are provided in various semiconductor devices and each of the semiconductor devices may include two or more such electric fuses.
Typically, an operation for writing given data by causing a current to flow through an electric fuse is performed using a large scale integration (LSI) tester. The LSI tester reads and checks the data, which has been written in two or more electric fuses provided in a semiconductor device, using a readout circuit in which the data is determined to be “0” or “1” based on the resistance value of each electric fuse.
Such semiconductor devices including electric fuses have been developed in a variety of ways. Known examples include a semiconductor device in which information on cutoff of an electric fuse is provided using a shift register and the cutoff of the electric fuse is controlled using an LSI tester.
Another example is a semiconductor device in which electric fuses to be cut off are divided into a plurality of groups and cutoff operations are sequentially performed for each of the groups.
As described above, electric fuses are generally provided in various semiconductor devices and utilized as nonvolatile storage elements for performing various functions. For example, a current of tens of milliamperes is desirably caused to flow through each of such electric fuses for tens of microseconds (μs) so that the electric fuses may be cut off.
Since the amount of a current that the LSI tester may supply is limited, the number of electric fuses that may be cut off at one time is also limited.
Accordingly, to cut off many electric fuses, the cutoff operations are desirably divided and performed at two or more times, and a current of tens of μs is desirably caused to flow through the electric fuses per series of the cutoff operations.
Typically, when two or more electric fuses provided in a semiconductor device are cut off using an LSI tester, the cutoff operations have been desirably divided and performed at two or more times in view of the amount of a current that the LSI tester may supply.
For example, in the electric fuse cutoff control circuit that Japanese Patent Application Laid-Open Publication No. 2006-197272 discusses, electric fuses to be cut off are divided into two or more groups in view of the amount of a current that an LSI tester may supply, cutoff operations are sequentially performed for each of the groups, and the cutoff operations are repeated before the number of electric fuses to be cut off becomes zero.
According to this example, however, since combinations of the electric fuses that may be concurrently cut off are fixed, there may be a case where only one electric fuse is cut off at one time and it takes much time to complete all of the cutoff operations for the electric fuses desired to be cut off.